package app

import (
	"crypto/rand"
	"encoding/base64"
	"errors"
	"io/ioutil"
	"log"
	"math/big"
	"net"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"text/template"

	"github.com/braintree/manners"
	"github.com/elazarl/go-bindata-assetfs"
	"github.com/fatih/camelcase"
	"github.com/fatih/structs"
	"github.com/gorilla/websocket"
	"github.com/hashicorp/hcl"
	"github.com/kr/pty"
)

type App struct {
	command []string
	options *Options

	upgrader  *websocket.Upgrader
	server    *manners.GracefulServer
	authToken string

	titleTemplate *template.Template
}

type Options struct {
	Address         string
	Port            string
	PermitWrite     bool
	EnableBasicAuth bool
	Credential      string
	EnableRandomUrl bool
	RandomUrlLength int
	IndexFile       string
	EnableTLS       bool
	TLSCrtFile      string
	TLSKeyFile      string
	TitleFormat     string
	EnableReconnect bool
	ReconnectTime   int
	Once            bool
	Preferences     map[string]interface{}
}

var DefaultOptions = Options{
	Address:         "",
	Port:            "8080",
	PermitWrite:     false,
	EnableBasicAuth: false,
	Credential:      "",
	EnableRandomUrl: false,
	RandomUrlLength: 8,
	IndexFile:       "",
	EnableTLS:       false,
	TLSCrtFile:      "~/.gotty.crt",
	TLSKeyFile:      "~/.gotty.key",
	TitleFormat:     "GoTTY - {{ .Command }} ({{ .Hostname }})",
	EnableReconnect: false,
	ReconnectTime:   10,
	Once:            false,
	Preferences:     make(map[string]interface{}),
}

func New(command []string, options *Options) (*App, error) {
	titleTemplate, err := template.New("title").Parse(options.TitleFormat)
	if err != nil {
		return nil, errors.New("Title format string syntax error")
	}

	return &App{
		command: command,
		options: options,

		upgrader: &websocket.Upgrader{
			ReadBufferSize:  1024,
			WriteBufferSize: 1024,
			Subprotocols:    []string{"gotty"},
		},
		authToken: generateRandomString(20),

		titleTemplate: titleTemplate,
	}, nil
}

func ApplyConfigFile(options *Options, filePath string) error {
	filePath = ExpandHomeDir(filePath)
	if _, err := os.Stat(filePath); os.IsNotExist(err) {
		return err
	}

	fileString := []byte{}
	log.Printf("Loading config file at: %s", filePath)
	fileString, err := ioutil.ReadFile(filePath)
	if err != nil {
		return err
	}

	config := make(map[string]interface{})
	hcl.Decode(&config, string(fileString))
	o := structs.New(options)
	for _, name := range o.Names() {
		configName := strings.ToLower(strings.Join(camelcase.Split(name), "_"))
		if val, ok := config[configName]; ok {
			field, ok := o.FieldOk(name)
			if !ok {
				return errors.New("No such option: " + name)
			}

			var err error
			if name == "Preferences" {
				prefs := val.([]map[string]interface{})[0]
				htermPrefs := make(map[string]interface{})
				for key, value := range prefs {
					htermPrefs[strings.Replace(key, "_", "-", -1)] = value
				}
				err = field.Set(htermPrefs)
			} else {
				err = field.Set(val)
			}

			if err != nil {
				return err
			}

		}
	}

	return nil
}

func (app *App) Run() error {
	if app.options.PermitWrite {
		log.Printf("Permitting clients to write input to the PTY.")
	}

	if app.options.Once {
		log.Printf("Once option is provided, accepting only one client")
	}

	path := ""
	if app.options.EnableRandomUrl {
		path += "/" + generateRandomString(app.options.RandomUrlLength)
	}

	endpoint := net.JoinHostPort(app.options.Address, app.options.Port)

	wsHandler := http.HandlerFunc(app.handleWS)
	customIndexHandler := http.HandlerFunc(app.handleCustomIndex)
	authTokenHandler := http.HandlerFunc(app.handleAuthToken)
	staticHandler := http.FileServer(
		&assetfs.AssetFS{Asset: Asset, AssetDir: AssetDir, Prefix: "static"},
	)

	var siteMux = http.NewServeMux()

	if app.options.IndexFile != "" {
		log.Printf("Using index file at " + app.options.IndexFile)
		siteMux.Handle(path+"/", customIndexHandler)
	} else {
		siteMux.Handle(path+"/", http.StripPrefix(path+"/", staticHandler))
	}
	siteMux.Handle(path+"/auth_token.js", authTokenHandler)
	siteMux.Handle(path+"/js/", http.StripPrefix(path+"/", staticHandler))
	siteMux.Handle(path+"/favicon.png", http.StripPrefix(path+"/", staticHandler))

	siteHandler := http.Handler(siteMux)

	if app.options.EnableBasicAuth {
		log.Printf("Using Basic Authentication")
		siteHandler = wrapBasicAuth(siteHandler, app.options.Credential)
	}

	wsMux := http.NewServeMux()
	wsMux.Handle("/", siteHandler)
	wsMux.Handle(path+"/ws", wsHandler)
	siteHandler = (http.Handler(wsMux))

	siteHandler = wrapLogger(siteHandler)

	scheme := "http"
	if app.options.EnableTLS {
		scheme = "https"
	}
	log.Printf(
		"Server is starting with command: %s",
		strings.Join(app.command, " "),
	)
	if app.options.Address != "" {
		log.Printf(
			"URL: %s",
			(&url.URL{Scheme: scheme, Host: endpoint, Path: path + "/"}).String(),
		)
	} else {
		for _, address := range listAddresses() {
			log.Printf(
				"URL: %s",
				(&url.URL{
					Scheme: scheme,
					Host:   net.JoinHostPort(address, app.options.Port),
					Path:   path + "/",
				}).String(),
			)
		}
	}

	var err error
	app.server = manners.NewWithServer(
		&http.Server{Addr: endpoint, Handler: siteHandler},
	)
	if app.options.EnableTLS {
		crtFile := ExpandHomeDir(app.options.TLSCrtFile)
		keyFile := ExpandHomeDir(app.options.TLSKeyFile)
		log.Printf("TLS crt file: " + crtFile)
		log.Printf("TLS key file: " + keyFile)
		err = app.server.ListenAndServeTLS(crtFile, keyFile)
	} else {
		err = app.server.ListenAndServe()
	}
	if err != nil {
		return err
	}

	log.Printf("Exiting...")

	return nil
}

func (app *App) handleWS(w http.ResponseWriter, r *http.Request) {
	log.Printf("New client connected: %s", r.RemoteAddr)

	if r.Method != "GET" {
		http.Error(w, "Method not allowed", 405)
		return
	}

	conn, err := app.upgrader.Upgrade(w, r, nil)
	if err != nil {
		log.Print("Failed to upgrade connection")
		return
	}

	_, initMessage, err := conn.ReadMessage()
	if err != nil || string(initMessage) != app.authToken {
		log.Print("Failed to authenticate websocket connection")
		return
	}

	cmd := exec.Command(app.command[0], app.command[1:]...)
	ptyIo, err := pty.Start(cmd)
	if err != nil {
		log.Print("Failed to execute command")
		return
	}
	log.Printf("Command is running for client %s with PID %d", r.RemoteAddr, cmd.Process.Pid)

	context := &clientContext{
		app:        app,
		request:    r,
		connection: conn,
		command:    cmd,
		pty:        ptyIo,
	}

	context.goHandleClient()
}

func (app *App) handleCustomIndex(w http.ResponseWriter, r *http.Request) {
	http.ServeFile(w, r, ExpandHomeDir(app.options.IndexFile))
}

func (app *App) handleAuthToken(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("var gotty_auth_token = '" + app.authToken + "';"))
}

func (app *App) Exit() (firstCall bool) {
	if app.server != nil {
		log.Printf("Received Exit command, waiting for all clients to close sessions...")
		return app.server.Close()
	}
	return true
}

func wrapLogger(handler http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		log.Printf("%s %s", r.Method, r.URL.Path)
		handler.ServeHTTP(w, r)
	})
}

func wrapBasicAuth(handler http.Handler, credential string) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		token := strings.SplitN(r.Header.Get("Authorization"), " ", 2)

		if len(token) != 2 || strings.ToLower(token[0]) != "basic" {
			w.Header().Set("WWW-Authenticate", `Basic realm="GoTTY"`)
			http.Error(w, "Bad Request", http.StatusUnauthorized)
			return
		}

		payload, err := base64.StdEncoding.DecodeString(token[1])
		if err != nil {
			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
			return
		}

		if credential != string(payload) {
			w.Header().Set("WWW-Authenticate", `Basic realm="GoTTY"`)
			http.Error(w, "authorization failed", http.StatusUnauthorized)
			return
		}

		log.Printf("Basic Authentication Succeeded: %s", r.RemoteAddr)
		handler.ServeHTTP(w, r)
	})
}

func generateRandomString(length int) string {
	const base = 36
	size := big.NewInt(base)
	n := make([]byte, length)
	for i, _ := range n {
		c, _ := rand.Int(rand.Reader, size)
		n[i] = strconv.FormatInt(c.Int64(), base)[0]
	}
	return string(n)
}

func listAddresses() (addresses []string) {
	ifaces, _ := net.Interfaces()

	addresses = make([]string, 0, len(ifaces))

	for _, iface := range ifaces {
		ifAddrs, _ := iface.Addrs()
		for _, ifAddr := range ifAddrs {
			switch v := ifAddr.(type) {
			case *net.IPNet:
				addresses = append(addresses, v.IP.String())
			case *net.IPAddr:
				addresses = append(addresses, v.IP.String())
			}
		}
	}

	return
}

func ExpandHomeDir(path string) string {
	if path[0:2] == "~/" {
		return os.Getenv("HOME") + path[1:]
	} else {
		return path
	}
}